Halogen-substituted aliphatic hydrocarbons, especially chlorine-substituted compounds having 1 or 2 carbon atoms, have been widely used as a solvent in detergents because of their high dissolving power for organic substances such as fats and oils. For example, trichloroethylene, a typical chlorine-substituted ethylene, is sparingly water soluble and highly volatile and has been used chiefly as a solvent for dry cleaning or for degreasing in the electromachinery industry or the semiconductor industry. Trichloroethylene exhibits an inhibitory action on the central nervous system and an anesthetic action similar to chloroform, and has been reported to be a mutagen (teratogen) and carcinogen. Because of its toxicity, trichloroethylene, should be collected and recycled. Should trichloroethylene be present in waste water, it would accumulate in soil or in groundwater since it is not easily degraded in nature and is sparingly soluble in water. To remedy trichloroethylene pollution, it is recovered physically, for example, by a method comprising exposing pumped groundwater to air and collecting the volatized trichloroethylene from the air, by a method in which pumped groundwater is treated with activated carbon, or by a method of adsorbing and removing a soil gas under reduced pressure. The thus recovered trichloroethylene is then decomposed by combustion or by a photochemical means using a catalyst.
It has been found that some anaerobic bacteria living in soil produce, from trichloroethylene, vinyl chloride (chloroethylene) or dichloroethylene which are more mutagenic (teratogenic) or carcinogenic than trichloroethylene [see E. J. Bouwer and P. L. McCarty, Appl. Environ. Microbiol., 45, 1286 (1983), T. M. Vogel, C. S. Criddle and P. L. McCarty, Environ. Sci. Technol., 21, 722 (1987) and Appl. Environ. Microbiol., 49, 1080 (1985)]. Thus, the immediate degradative treatment of trichloroethylene pollution is of increasing demand. Great expectations have recently been held for use of microorganisms for the purpose of degrading trichloroethylene which has accumulated in groundwater and is diffused over a wide area in a relatively low concentration.
Besides the anaerobic bacteria capable of producing vinyl chloride (chloroethylene) or dichloroethylene from trichloroethylene, it has been reported that some aerobic bacteria are capable of degrading halogen-substituted aliphatic hydrocarbons. With respect to the biological degradation of trichloroethylene using aerobic microorganisms, use of microorganisms capable of producing an enzyme catalyzing oxidation of ammonia, methane or a methyl group, i.e., an enzyme for oxidizing an atomic group containing no double bond, has been reported. Such microorganisms include toluene-assimilating microorganisms capable of producing toluene dioxygenase [see G. J. Zylstra, L. P. Wackett and D. T. Gibson, Appl. Environ. Microbiol., 55, 3162 (1989)], toluene-assimilating microorganisms capable of producing toluene monooxygenase [see R. B. Winter, K-M. Yen and B. D. Ensley, Bio/Technol7,282 (1989)], methane-assimilating microorganisms capable of producing methane monooxygenase [see R. Oldenhuis, R. L. J. M. Vink, D. B. Janssen, and B. Witholt, Appl. Environ. Microbiol., 55, 2819 (1989)], and ammonia-assimilating microorganisms capable of producing ammonia monooxygenase [see T. Vannelli, M. Logan, D. M. Arciero, and A. B. Hooper, Appl. Environ. Microbiol., 56, 1169 (1990)]. Aside from these enzymes for converting a hydrogen atom of hydrocarbons to a hydroxyl group, biological technology for degrading trichloroethylene utilizing other hydrocarbon oxidizing enzymes has not yet been established. In particular, development of a biological method suitable for degrading trichloroethylene at high efficiency has been demanded.
In addition, it has been demanded that a method for biologically degrading not only trichloroethylene but other chlorine-substituted ethylenes, such as vinyl chloride (chloroethylene) and dichloroethylene, which are produced from trichloroethylene by the action of anaerobic bacteria be developed.